GRANJENO, Texas  Founded 240 years ago, this sleepy Texas town along the Rio Grande has outlasted the Spanish, then the Mexicans and then the short-lived independent Republic of Texas. But it may not survive the U.S. government's effort to secure the Mexican border with a steel fence.

A map obtained by The Associated Press shows that the double- or triple-layer fence may be built as much as two miles from the river on the U.S. side of the Rio Grande, leaving parts of Granjeno and other nearby communities in a potential no-man's-land between the barrier and the water's edge.

Based on the map and what the residents have been told, the fence could run straight through houses and backyards. Some fear it could also cut farmers off from prime farmland close to the water.

"I don't sleep right because I'm worried," said Daniel Garza, a 74-year-old retiree born and raised in Granjeno. Garza said federal agents told him that the gray brick house he built just five years ago and shares with his 72-year-old wife is squarely in the fence's path.

"No matter what they offer, I don't want to move, I don't want to leave," Garza said, his eyes watering.

Congress has authorized $1.2 billion for 700 miles of fence at the Mexican border to keep out illegal immigrants and drug smugglers. The plans call for about 330 miles of virtual fences — cameras, underground sensors, radar and other technology — and 370 miles of real fences. About 70 miles of real fence are set to be built in the Rio Grande Valley, at the southeastern tip of Texas, by the end of 2008.

The Rio Grande has been the international boundary since the Treaty of Guadalupe-Hidalgo in 1848 ended the Mexican-American War. But officials say that putting the fence right up against the river could interfere with its flow during a flood and change its course, illegally altering the border.

The map obtained by the AP shows seven stretches of proposed fence in the Rio Grande Valley, including one section that could cut through the property of about 35 of Granjeno's nearly 100 houses. City leaders and residents say federal officials have shown them the same map.

Exactly how many Rio Grande Valley residents could lose some or all of their property is unclear. The map does not have a lot of detail, and depicts only one portion of the valley, which has about 2 million people overall.

Local residents, many of whom have put "No Border Wall" signs on their cars and in their yards, say they have been assured they will be compensated at fair market value for any property taken by the U.S. government. But that has not given them much comfort.

"We want to be safe, but it's just that this is not a good plan," said Cecilia Benavides, whose riverfront land in Roma, about 50 miles upriver from Granjeno, was granted to the family by the Spanish in 1767. "It gives Mexico the river and everything that's behind that wall. It doesn't make any sense to me."

Michael Friel, a Customs and Border Protection spokesman in Washington, said the maps are preliminary and no final decisions on the route of the fence have been made. But he said the maps reflect the government's judgment of how best to secure the border against intruders.

"Our agency, Customs and Border Protection, has an obligation to secure our nation's border and we take that obligation, or that responsibility, very seriously," Friel said.

The fence would be at least 15 feet high and capable of withstanding a crash of a 10,000-pound vehicle going 40 mph, according to the Department of Homeland Security.

Exactly what it would look like has not been decided, but it could consist of concrete-filled steel posts a few inches apart, or perhaps sheet metal with small openings. It would not be continuous, but would instead be broken up in several sections of various length.

What will happen to the land between the fence and the river is the biggest question for landowners in border towns like Granjeno, a town of three streets and about 400 people situated in a mostly corn-growing region of the Rio Grande Valley.

J.D. Salinas, the top elected official in Hidalgo County, said he can't get an answer no matter how many times he asks.

"Are we going to lose prime farmland because they are going to build a structure that's not going to work?" Salinas asked. "You're moving the border, basically two miles. You're giving it up to Mexico, and the U.S.-Mexico treaties say you are not supposed to do that."

Local officials also fear the fence could cut off access to drinking water that is pumped from the river and piped in to 35,000 homes in the Rio Grande Valley. They fear that town officials will not be allowed to set foot inside the no-man's-land to repair any pumps that might fail.

Homeland Security documents on a department website say that "in some cases, secure gates will be constructed to allow land owners access to their private property near the Rio Grande." But the documents offer few details.

"They said there's going to be gates, and I said, 'That's wonderful. What kind of gates?"' said Noel Benavides, Cecilia Benavides' husband. The only specific type described, he said, was an electronic gate.

"That requires power. What happens when it floods?" Benavides said he asked federal officials. He never got an answer.

Granjeno Mayor Alberto Magallan said his small town wants to fight. But with only one business — an agricultural trucking company and bar — and a per capita income of $9,000, it is unlikely they can afford to do anything but sell.

Manuel Olivarez Jr., a 63-year-old lumber salesman, said that his daughter's and brother's homes would be spared, but that the fence would run through their backyards. And Olivarez worries the Border Patrol is likely to pass very close to his daughter's house every day.

"Probably if she sticks out her hand from the back door, a Border Patrol Jeep will be hit her," Olivarez said with a nervous laugh.

Gloria Garza, Daniel Garza's niece, said she worries the border fence will eventually destroy the town where she has lived all her life.

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